1. Field of the Invention
The present invention relates to a processed pigment, a pigment-dispersed composition and a colored photosensitive composition using the same, a color filter using the colored photosensitive composition, and a liquid crystal display element and a solid image pickup element provided with the color filter.
2. Description of the Related Art
A color filter is produced by preparing a pigment-dispersed composition in which an organic pigment or an inorganic pigment is dispersed, or a colored photosensitive composition containing a polyfunctional monomer, a polymerization initiator, an alkali-soluble resin, and other components, and forming a colored pattern or a black matrix by a photolithography method or an ink jet method using the composition.
In recent years, uses for liquid crystal display elements (LCDs) have expanded beyond monitors to include television (TVs). Together with this expansion has come increased demands for improvements in the properties of color filters with respect to chromacity and contrast. Similarly, demands have increased for color filters used in image sensors (solid image pickups) to have improved color properties such as reduced color variation and improved color resolution.
In response to the aforementioned requirement, it has been further required that the pigment contained in the colored photosensitive composition is dispersed in a finer state (better dispersibility), and is dispersed in a more stable state (better dispersion stability). When dispersibility of the pigment is insufficient, problems occur such as a fringe (serration at an edge) or surface irregularity generated at a colored pixel formed by a photolithography method, and developer (residue) remaining on the substrate, whereby chromaticity or dimensional precision of a manufactured color filter is reduced, and contrast is remarkably deteriorated.
When the dispersion stability of a pigment is insufficient, then, in particular during the manufacturing processes of the color filter, uniformity of layer thickness in the colored curable composition coating process may readily fall, sensitivity in the exposure process may readily fall, and/or the alkali solubility in the development process may readily fall. When there is poor dispersion stability of the pigment, this may cause aggregation of the components of the colored curable composition and cause a rise in viscosity over time, leading to an extremely short pot-life.
Although it is somewhat effective to make the particle size of a pigment finer in order to improve coloring characteristics, such as the contrast of a color filter, since the surface area of the pigment particles becomes larger when the particle size of a pigment is made finer, the cohesive force between pigment particles increases, and it has been difficult in many cases to achieve both a high level of dispersibility and a high level of dispersion stability.
The following techniques are known for making pigment particles finer and for improving the dispersibility of pigment particles. Generally, a method (salt milling method) is known for making the primary particles of a pigment finer by mechanically mixing and kneading, using a kneader or the like, a pigment, a water soluble inorganic salt, and a water soluble organic solvent which does not dissolve substantially such as an inorganic salt. The primary particle mixture of the obtained fine pigment is added to water and agitated, using a mixer or the like, to form a slurry state. Next, by filtering this slurry, washing with water and drying, a fine pigment is obtained as a secondary aggregate, which is an aggregate of the primary particles of the pigment. The dispersion process in ordinary dispersion machines, such as a sand mill, a ball mill, or the like, is a process that loosens the secondary aggregate, which is an aggregate of the primary particles of pigment, obtaining a dispersion body state that is close to that of the primary particles.
However, when a primary particle of the pigment is miniaturized, the particle is easily aggregated, and a slurry, or an aggregate (secondary aggregate) is easily generated when drying. In addition, as the primary particle of the pigment is further miniaturized, strong secondary aggregation occurs. For this reason, it is generally very difficult to re-disperse the miniaturized pigment to a primary particle. Since a color filter formed using a dispersion in which a large amount of a secondary aggregate is present has great scattering of light, remarkably reduced contrast, and produces fluctuations in color density, a composition as a pigment-dispersed composition in which a primary particle is stably dispersed without aggregation is preferable, and also preferable is that the composition is easily handled.
For the purpose of suppressing strong secondary aggregation of this miniaturized pigment, a technique of adding rosin or a rosin derivative, or a non-water-soluble monomer or an oligomer to treat the pigment at a salt milling step, and using a dispersion of the pigment to obtain a color filter having a high contrast, has been proposed (see Japanese Patent No. 3130217 and Japanese Patent Application Laid-Open (JP-A) No. 2004-233727).
In addition, a technique of using a polymer compound having a heterocycle on a side chain as a pigment dispersion at a dispersion step, to obtain a color filter having a high contrast by a pigment-dispersed composition excellent in dispersion stability, and a colored photosensitive composition using the same, has been proposed (e.g. see JP-A No. 2003-26950).
However, these methods may not sufficiently respond to the further increased demands with respect to contrast from the market; moreover, higher dispersity and dispersion stability in the fine pigment have been desired.